Chemicals can reach man through a variety of media--air, water, food, or a combination of them. Assessing the probable route and level of exposure, and the subsequent health hazard of a chemical to man requires and understanding of its behavior in environmental and biological phases. Sorption, evaporation, bioaccumulation, and degradation influence the accumulation and distribution of a chemical. Similarly, in the biological action of a compound, three aspects may be categorized, namely transport, binding/partitioning, and reaction. The same physico-chemical factors and molecular parameters that relate to environmental behavior are operative in the biological system. Previous studies in simple systems have demonstrated a number of fundamental relationships between the physico-chemical properties of the compound and its environmental behavior (e.g., bioaccumulation, evaporation, and sorption by soil). The utility of this approach can be enhanced as a wider variety of compounds are studied, and as the concepts can be applied is determined in large part by the accuracy of the appropriate physical chemical parameters. Unfortunately, there is considerable uncertainty concerning some literature values, particularly for compounds of environmental significance. Consequently, further work is necessary to provide validated data for assessment needs.